If you've ever seen a gecko, you've probably noticed how excellent they are at not falling off of things. Researchers at the University of Massachusetts at Amherst have managed to create an adhesive based on gecko toes that works nearly as well as the real thing, and an index card of this stuff is powerful enough to stick you and six* of your most daring friends directly to a sheet of glass.
Geckos, we should point out, don't "stick" to things in that their feet aren't "sticky" in the way that you normally think of adhesives like tape or glue as being sticky. It might be more accurate to say that geckos "bond" to surfaces temporarily, relying on weak attractive forces between molecules called Van der Waals forces. If you've got enough contact between your molecules and the molecules of whatever you want to hang on to (the material doesn't matter), these forces can be very powerful, and geckos have no trouble hanging on to panes of glass with only one toe. And since there's no wet adhesive involved, it's easy for geckos to unbond themselves, and they don't leave behind messy trails of goop.
Image via Hizook
We've had a bit of a tough time reverse-engineering gecko toes to achieve this same effect. Gecko toes are very complex, and they're covered with tiny little nanoscopic hairs with pads on the end called spatulae. While we've been able to duplicate the structure of these hairs with synthetic materials, the difficult part has been getting the artificial gecko feet to behave as pliably and adaptably as the real thing (although we're getting close).
The team at UMass Amherst has created a new material that they're calling "Geckskin" that gets around some of these anatomical roadblocks by getting rid of the tiny hairs entirely, replacing them with a soft adhesive pad woven into a stiff fabric backing. This mimics the basic functionality of a gecko foot without the complexity, allowing the material to flexibly drape over a surface and maximize molecule-on-molecule contact, while still being fast and easy to remove. A 16 square-inch pad of Geckskin can hold 700 pounds, and you can lift it off and reattach it to surfaces (smooth surfaces) as many times as you like without leaving behind any gunk.
If you're thinking to yourself about now, "boy, it sure would be awesome to put this stuff on gloves and shoes and make a Spiderman suit out of it," DARPA is way ahead of you. This research is funded under DARPA's Z-Man program, which is trying to "develop biologically inspired climbing aids to enable soldiers to scale vertical walls constructed from typical building materials, without using ropes or ladders. The overall goal is to enable a soldier to scale a vertical surface while carrying a full combat load using Z-Man technologies." That's right folks, it's not a comic book, it's DARPA.
*We're just assuming that you and all your friends are 98-pound weaklings like we are.